uraae. 

 Date. . 



EXERCISE 20 



(53) 



Soil Surface and Percolation 



Purpose. — To study the relationship between soil surface and the percolation 

 of free water. 



PLAN 



1. Secure three or more small glass tubes of uniform length (about one 



foot) and place them in a jar of water deep enough 

 to fill them to the top. Place the finger or palm of 

 the hand against the top of the tubes and with the 

 other hand remove the bundle of tubes from the 

 jar of water. Hold the bundle in a vertical position 

 and note that the water remains in the tubes. Now 

 remove the hand from the top and see how quickly 

 the water descends. 



2. Fill two soil tul)es (Fig. 16) with clay loam, packing 



them alike. Set them in a jar of water until satu- 

 rated. Loosen the surface of one with a kitchen fork; 

 smooth the surface of the other with the bowl of a 

 wet spoon to avoid the free entrance of air. Then set 

 the tubes of soil so as to drain into beaker glasses. ^"^"^1 



Compare the rates of drainage of free water from * 



the two tubes as a result of the difference in treat- soiftui>e!2''^^2™wi'th 



perforated bottom, use- 

 ful in many exercises. 



ment of the surfaces^ 



QUESTIONS 



1. Why does the exclusion of air at the top of the tubes retard percolation? 



2. Does a heavy soil beaten by rain or puddled by free water stantling on 



the surface tend to exclude the air? Explain. 



3. What treatment can be given to the surface of field soils after heavy rains 



before they are quite dry enough to plow well? 



4. Does a heavy, thick, dry, crust tend to exclude air from the soil more than 



a loosened surface? Explain. 



5. Would harrowing tend to let the free water downward? Whv? 



